1. Field of the Invention
The present invention relates to a process for treatment of organic wastewater, and particularly to a process for biological treatment of organic wastewater such for example as manure-washing wastewater discharged from the livestock industry or wastewater discharged from the food industry though the organic wastewater is not particularly limited thereto.
2. Related Art
High concentrations of organic matter and nitrogen components such as organic nitrogen and ammonia are contained in organic wastewaters such for example as manure-washing wastewater discharged from the livestock industry and wastewater discharged from the food industry. Thus, such organic wastewaters are desired to be discharged to environment after they are rendered harmless.
For example, wastewater resulting from washing livestock manure (feces and urine) with water is treated by a combination of a plurality of treatment methods, examples of which include solid-liquid separation, composting, evaporation and concentration, and biological treatment.
In regions having a large farming area, the wastewater resulting from washing livestock manure with water is mostly biologically treated in lagoons requiring not many hands and involving easy maintenance and control thereof. Oxygen supply for decomposition of contaminants in a common lagoon without aeration relies only on diffusion of oxygen from the surface of the lagoon, or pond. Hence, the treatment is so inefficient that the resultant treated water in the lagoon still contains a high concentration of undecomposed organic matter. Treatment in this kind of lagoon is a combination of aerobic biological treatment with anaerobic biological treatment. Since the anaerobic biological treatment is dominant in this case, however, organic nitrogen and ammonium nitrogen cannot well be removed. In general, the treated water obtained in the lagoon is mostly percolated downward through the soil either as it is or after it is sprinkled over the ground or used for irrigation of a plowed field, or evaporated for final disposal thereof.
Examples of lagoons improved over the foregoing common lagoon include an aerated lagoon with an aerator(s) capable of positively dissolving molecular oxygen in lagoon water, a lagoon capable of utilizing molecular oxygen generated by growth of aquatic plants such as algae, and a lagoon having an aerobic zone capable of nitrification with the aid of aeration of the zone with an agitating aerator and an anaerobic zone capable of denitrification. In all such lagoons, however, the efficiency of decomposition of organic matter as well as the efficiency of nitrification and denitrification is not so well because of a low microorganism concentration therein. Accordingly, these lagoons may leak harmful substances such as undecomposed organic matter, organic nitrogen, ammonium nitrogen, and nitric nitrogen (nitrate nitrogen) and nitrous nitrogen (nitrite nitrogen) both formed by nitrification of ammonium nitrogen to the environment and in particular to groundwater when it rains and/or the resultant treated water percolates through the soil. This has become a problem. The contamination of groundwater is a problem in particular because strongly toxic nitrous acid contaminates drinking water. One cause of this is percolated water from lagoons.
On the other hand, composting, evaporation and concentration, and the like method involve emission of malodors, while treated water obtained only through a simple treatment such as solid-liquid separation, if discharged to a drinking water source such as a river or a lake, becomes a problem because of a high possibility that protozoa such as Cryptosporidium and parasites might be contained in such treated water.
In stock farms, which are generally run by a small number of people in many cases, treatment processes such as an activated-sludge process, which require considerable labor for maintenance and control thereof, are impractical. Furthermore, since protozoa cannot be removed by the activated-sludge process, discharge of treated water obtained by this process to rivers and the like presents a problem.
An object of the present invention is to provide a wastewater treatment process capable of efficient biological treatment of organic wastewaters such as wastewater from the livestock industry and wastewater from the food industry for making the wastewaters harmless.